Method of manufacturing a custom corner attach heat sink design for a plastic ball grid array integrated circuit package

ABSTRACT

An integrated circuit package. The package includes a substrate which has a first surface, a second opposite surface and four corners. Each corner has a conductive plane and at least one via. The vias connect the conductive planes of the first surface with corresponding conductive planes located on the second surface of the substrate. An integrated circuit is mounted to the first surface of the substrate and enclosed by plastic. Solder balls are attached to the conductive planes and a number of individual solder pads located on the second surface of the package. The contacts are connected to a printed circuit board. A lid is attached to the conductive planes at the four corners of the substrate. Some of the heat generated by the integrated circuit conducts through the substrate and into the printed circuit board. Some of the heat within the substrate conducts into the lid through the conductive planes located at the corners of the package. The present invention thus provides two thermal paths, the printed circuit board and the lid, from the substrate of a plastic integrated circuit package.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of Ser. No. 08/832,417 filed Apr. 2,1997, now U.S. Pat. No. 5,898,219 issued Apr. 27, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an integrated circuit package.

2. Description of Related Art

Integrated circuits are typically assembled into a package that ismounted to a printed circuit board. There are a number of differenttypes of packages including quad flat pack (QFP), pin grid array (PGA)and ball grid array (BGA). BGA packages include a number of solder ballsthat are soldered to corresponding solder pads located on the bottomsurface of a substrate. The solder balls are reflowed to attach thesubstrate to a printed circuit board.

An integrated circuit is mounted to a top surface of the substrate. Theintegrated circuit is connected to bond pads located on the top surfaceof the substrate by wire bonds. The bond pads are connected to thesolder pads on the second surface by a number of vias and routing tracesformed within the substrate. The integrated circuit is enclosed by amolded plastic material.

The heat generated by the integrated circuit conducts into the printedcircuit board through the vias, the routing traces and the solder balls.The vias and routing traces have a relatively high thermal impedance.The high thermal impedance creates an undesirable temperaturedifferential between the circuit board and the integrated circuit. Thehigh temperature differential may create junction temperatures whichexceed the recommended operating limits of the integrated circuit. Somepackages incorporate heat slugs which remove heat from the top surfaceof the integrated circuit die. Heat slugs add to the complexity and costof mass producing the package. It would be desirable to provide anintegrated circuit package that provides an alternate thermal path forheat to flow from the substrate to reduce the overall thermal impedanceof the package.

SUMMARY OF THE INVENTION

The present invention is an integrated circuit package. The packageincludes a substrate which has a first surface, a second oppositesurface and a corner. Each corner has a conductive plane located on thefirst surface of the substrate. An integrated circuit is mounted to thefirst surface of the substrate. A lid is attached to the conductiveplane at the corner of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an integrated circuit package of thepresent invention;

A FIG. 2 is a top view of a substrate of the package;

FIG. 3 is a bottom view of the substrate;

FIG. 4 is a cross-sectional view of an alternate embodiment of a packagewith a heat sink.

DESCRIPTION OF THE INVENTION

Referring to the drawings more particularly by reference numbers, FIGS.1-3 show an integrated circuit package 10 of the present invention. Theintegrated circuit package 10 includes a substrate 12 which has a firstsurface 14 and an opposite second surface 16.

As shown in FIG. 2, the first surface 14 has a number of conductiveplanes 18 at the four corners 20 of the substrate 12. The first surface14 also has a conductive ring 22 and a plurality of bond pads 24. As oneembodiment, the conductive ring 22 is dedicated to electrical ground andconnected to the conductive planes 18. The bond pads 24 are preferablyarranged into staggered rows to accommodate the conductive planes 18.The conductive planes 18 are coupled a number of vias 26 that extendthrough the substrate 12. The bond pads 24 are connected to the vias 26by routing traces 28.

As shown in FIG. 3, the vias 26 are connected to a plurality of solderpads 30 located on the second surface 16 of the substrate 12. The solderpads 30 preferably have an elliptical shape to increase the peelstrength of the pads 30. The second surface 16 also has a plurality ofconductive planes 32 located at the four corners 20 of the substrate 12.The conductive planes 32 of the second surface 16 are electrically andthermally coupled to the conductive planes 18 of the first surface 14 bythe vias 26.

Referring to FIG. 1, an integrated circuit 34 is mounted to the firstsurface 14 of the substrate 12 and enclosed by plastic 36. Theintegrated circuit 34 is connected to the bond pads 24 and conductivering 22 by a plurality of bond wires 38. The integrated circuit 34 maybe a microprocessor, although it is to be understood that the circuit 34may be any active or passive electrical device(s).

The plastic covered integrated circuit 34 is enclosed by a thermallyconductive lid 40. The conductive lid 40 is attached to the conductiveplanes 18 at the four corners 20 of the substrate 12. The lid 40 may beattached to the planes 18 with a thermally conductive adhesive or epoxy42.

Contacts 44 are attached to the solder pads 30 located on the secondsurface 16 of the substrate 12. The contacts 44 are attached to aprinted circuit board 46. The contacts 44 are preferably solder ballsthat are initially attached to the solder pads 30 and then reflowed toattach the package 10 to the printed circuit board 46. The integratedcircuit 34 is electrically connected to the printed circuit board 46through the bond wires 38, bond pads 24, vias 26, solder pads 30 andcontacts 44. Although a ball grid array (BGA) type of package is shownand described, it is to be understood that other types of packages canbe implemented with the present invention.

The heat generated by the integrated circuit 34 will flow into thesubstrate 12. Some of the heat will flow through the substrate 12 andinto the circuit board 46. Some of the heat within the substrate 12 willflow into the conductive planes 18 and the lid 40 where the heat isremoved by forced and/or natural convection. The lid 40 provides anadditional thermal path which can efficiently remove heat from a plasticintegrated circuit package.

The package 10 can be assembled by mounting and wire bonding theintegrated circuit 34 to the substrate 12. The integrated circuit 34 isenclosed by molded plastic 36. The lid 40 is then attached to theconductive planes 18 at the four corners of the substrate 12. Thecontacts 44 are attached to the solder pads 30. The package 10 is thenmounted to the printed circuit board 46 by reflowing the contacts 44onto the board 46.

FIG. 4 shows an alternate embodiment, wherein a heat sink 48 is attachedto the thermally conductive lid 40. The heat sink 48 improves the heattransfer rate from the package 10 to the surrounding ambient.

What is claimed is:
 1. A method for assembling an integrated circuitpackage, the method comprising:providing a substrate which has a firstsurface, an opposite second surface and four corners; placing aconductive plane at each corner of the first surface of the substrate;placing a conductive ring on the first surface of the substrate, theconductive ring coupled to the conductive planes and surrounding anintegrated circuit; mounting the integrated circuit to the first surfaceof the substrate to be surrounded by and coupled to the conductive ring;and, attaching a thermally conductive lid to the conductive planes atthe four corners of the substrate.
 2. The method as recited in claim 1,further comprising attaching a contact to the second surface of thesubstrate.
 3. The method as recited in claim 2, further comprisingattaching a printed circuit board to the contact.
 4. The method asrecited in claim 1, further comprising enclosing the integrated circuitwith plastic before attaching the thermally conductive lid.
 5. A methodcomprising:providing a substrate including a first surface and a secondsurface; placing a thermally conductive ring on the first surface of thesubstrate; placing a thermally conductive plane at each corner of thefirst surface of the substrate, the thermally conductive plane beingconnected to the thermally conductive ring; placing an integratedcircuit on the first surface of the substrate, a perimeter of theintegrated circuit being surrounded by the thermally conductive ring;and attaching a thermally conductive lid to the thermally conductiveplanes to cover the integrated circuit.
 6. The method as recited inclaim 5, further comprising attaching a contact to the second surface ofsaid substrate.
 7. The method as recited in claim 5, further comprisingattaching a printed circuit board to the contact.
 8. The method asrecited in claim 5, further comprising enclosing the integrated circuitwith plastic before attaching the thermally conductive lid.
 9. Themethod as recited in claim 5, wherein the attaching of the thermallyconductive lid to the thermally conductive planes includes:placing athermally conductive adhesive on each of the thermally conductiveplanes; and attaching the thermally conductive lid to the thermallyconductive adhesive.
 10. The method as recited in claim 5; furthercomprising:attaching a heat sink to the thermally conductive lid.